[計(jì)算機(jī)]第3章補(bǔ)體系統(tǒng)-wenkub
2023-04-06 08:53:05 本頁面
【正文】 thway. The enzyme C1 is able to cleave C4 into C4a and C4b, as well as C2 into C2a and C2b. initiation I g M , I g G 1 a n d I g G 3C o m p l e m e n t fi x a ti o n b y a n ti b o d yIgG2 C 1 q b i n d i n g s i te sC e r ta i n b a c te r i a , v i r u s e s a n d u e a te c r y s ta l s c a n a c ti v a te c l a s s i c a l p a th w a y w i th o u t A b .M i c ro b eC 2 bC2C 2 aC 4 b1 1 0 k D3 4 k D7 4 k DC 1 qC 1 r C 1 sC a + +p r o te a s ea c ti v i tyC3 Convertase The enzyme C1 is able to cleave C4 into C4a and C4b. The C4b binds to adjacent proteins and carbohydrates on the surface of the antigen. C2 then binds to the C4b and C1 cleaves C2 into C2a and C2b. The C4b2a functions as a C3 convertase that can subsequently cleave hundreds of molecules of C3 into C3a and C3b. C 4 bC 2 aC 3 bC 5 aC 5 aC 5 bC5C 5 bC5 Convertase Much of the C3b binds to adjacent proteins and carbohydrates on the antigen to participate in opsonization while C3a can stimulate inflammatory responses. Some of the C3b binds to C4b2a to form C4b2a3b, a C5 convertase that can cleave C5 into C5a and C5b. C 5 bC6C7C8C9C9C8L YS I SM EM B R A N E A T T A C K C O M PL EX ( M A C )c o n fo r m a ti o n a l c h a n g e i n C 9 p r o te i n s tr u c tu r e H YD R O PH I L I C A M PH I PA T H I CThe Membrane Attack Complex (MAC) Causing Cell Lysis This C5b6789n, or membrane attack plex (MAC), puts pores into lipid bilayer membranes of human cells to which antibodies have bound. This results in cell lysis. MAC can also damage the envelope of enveloped viruses and put pores in the outer membrane and cytoplasmic membrane of gramnegative bacteria causing their lysis. p o r e? The electron micrograph shows holes punched through the cell wall of the bacterium Shigella dysenteriae by the terminal ponents of the plement system. Some of the holes are larger than expected for C9 channels and probably were enlarged later by the action of lysozyme Alternative (innate) pathways ? There is a spontaneous conversion of C3 to C3b. Ordinarily the C3b is quickly inactivated: the C3b binds to inhibitory proteins and sialic acid present on the surface of body39。 清除免疫復(fù)合物 三、連接天然免疫與獲得性免疫的橋梁 ? 參與免疫應(yīng)答的誘導(dǎo)： C3b參與捕捉、固定抗原，是抗原易被 APC處理 與提呈。C3a、 C4a、 C5a有此作用。 IgM（未與 Ag結(jié)合） IgM（已與 Ag結(jié)合） 活化階段 參與成分： C C C3 目的： 形成 C5轉(zhuǎn)化酶 過程： C4 C4b+C4a C2 C2b+C2a C4b2b C3 C3b+C3a C4b2b3b C1S C1S 活化階段 膜攻擊階段 參與成分： C C C C C9 目的： 形成 MAC 膜攻擊復(fù)合物 membrane attack plex, MAC 組成： C5b678 (9)n ，其中 C9分子可有 1215個 大?。?1011 nm 內(nèi)徑的小孔 效應(yīng)：胞內(nèi)滲透壓降低，細(xì)胞溶解 致死量鈣離子被動向胞內(nèi)彌散，細(xì)胞死亡 激活物： MBL MBL產(chǎn)生： 感染 巨噬細(xì)胞、中性粒細(xì)胞活化產(chǎn)生 TNF、 IL IL6等因子 肝細(xì)胞激活
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